Networking interface devices, e.g., routers, switches, network interface cards, etc. that facilitate transmission of data over a data communications network typically utilize a bias circuit, coupled to a line driver, to supply necessary power to facilitate transmission of data over the transmission line. An example of a conventional network device utilizing a static bias module is presented below, with reference to FIG. 1.
FIG. 1 is a block diagram of a conventional network interface device including a statically biased transmit module. In accordance with the illustrated example implementation, network interface device 100 couples a computing system (not shown) to network (not shown). The network interface device 100 is depicted comprising control logic 102, a receive module 104, a transmit module 106, memory 114 and one or more applications 116. As introduced above, transmit module 106 is intended to represent any of a number of transmitters which, in addition to conventional modulation, error correction and other processing attributes, includes a static bias module 108, coupled to a line driver 110, which is coupled to a network transmission line via an isolation transformer 112. As illustrated, a transmit module 106 may well include multiple bias module 108—line driver 110 pairs.
As introduced above, conventional network interface devices are typically designed with conventional static bias circuits, which are specified to accommodate a worst-case transmission requirement, and provide bias power to the line driver to facilitate such a worst-case transmission requirement even if that worst case transmission scenario only occasionally develops. An example of just such a worst-case transmission event is the baseline wander (BLW) high-power event.
Those skilled in the art will appreciate that a baseline wander high-power event occurs when transmitting a large number of consecutive ones (1) or zeroes (0) to the transmission line. When such a baseline wander event occurs, a DC offset is introduced into the transmitted signal, requiring additional power from the line driver 108. An example of a baseline wander event is illustrated with reference to FIG. 2, below.
FIG. 2 is a graphical illustration depicting introduction of a DC bias in a transmitted signal characteristic of a high-power event. As shown, FIG. 2 illustrates a data pattern 202 received for transmission. As depicted here, each logic high and/or low is intended to represent a number of 1's, or 0's, respectively. The illustrated pattern 204 depicts how the data pattern 202 is skewed with a DC offset after a long run of consecutive 1's or 0's. More particularly, with reference to numeral 206, a DC offset is denoted as the deviation of the signal from the dashed line.
Insofar as such high-power events, such as the illustrated baseline wander event 206 occur only occasionally, conventional bias modules effectively waste power by continuously supplying a heightened power level designed to support transmission through such a worst case condition.